1. Field of the Invention
The present invention relates to a lens system for use with an optical disk which is a high-density information recording medium.
2. Background of the Invention
A lens system which is used to read high-density information from an optical disk or to write such information into the disk is required to have a resolution of the order of 1 micrometer in order to detect high-density signals. However, the laser used as a light source for the operation of the optical disk sometimes experiences variations in wavelength and the variations may cause displacement of the focal point or aberrational variations, which will become a problem depending on the precision required of the optical disk.
The environment in which the lens system for use with an optical disk is put to service varies from time to time because the temperature to which the optical disk equipment is exposed undergoes great variations. Therefore, if the variations in temperature are extensive or if high precision is required for the operation of the optical disk, the displacement in focal point or aberrational variations that occur on account of such temperature variations will present a definite problem.
Most of the lens systems proposed to data for use with optical disks have been designed without taking into consideration the possibility of variations in wavelength (i.e., chromatic aberration) and temperature.